JP5440564B2 - Method for detecting crystal defects - Google Patents

Description

  The present invention relates to a method for detecting a crystal defect in a silicon single crystal wafer, and more particularly to a method for detecting a crystal defect by revealing it.

  Silicon single crystals tend to reduce the crystal defect size when the oxygen concentration is lowered. For example, in the case of a silicon single crystal wafer cut from a silicon single crystal having a low oxygen concentration such that the initial interstitial oxygen concentration is 8 ppma or less, particularly 5 ppma or less, BMD (Bulk Micro Defect), COP (Crystal Originated Particle) ), Since it is difficult to detect minute crystal defects such as “cavities”, it is extremely difficult to determine whether or not a cut silicon single crystal wafer is a defect-free region.

  For crystal defects that are difficult to detect because of their small size, a method is known in which detection is performed after performing a process for revealing the crystal defects.

  For example, Patent Document 1 discloses a silicon wafer evaluation method in which new oxygen precipitates are generated on a silicon wafer containing oxygen precipitates smaller than the lower limit size of oxygen precipitates detectable by a specific measuring device. The oxygen precipitate density in the silicon wafer is increased after all the oxygen precipitates smaller than the lower limit size are grown to a size that can be detected by the specific measuring device. A method for evaluating a silicon wafer is described in which the above-mentioned measurement is performed by the specific measuring device.

  Patent Document 2 discloses a method for proactively revealing crystal defects in a bulk silicon substrate, which is performed in a non-reducing atmosphere at a temperature in the range of 500 ° C. to 1300 ° C. A method of subjecting to a heat treatment referred to as "chemical heat treatment" is described. Specifically, this “sensible heat treatment” is performed in an atmosphere of oxygen, argon, nitrogen, or a mixture of the two.

JP 2002-246429 A JP 2007-273777 A

  As described above, in the case of a silicon single crystal wafer having a low oxygen concentration (low oxygen wafer), there is a problem that it is difficult to detect minute crystal defects such as BMD, COP, and “cavity”. In particular, since the defect size becomes smaller in a low-oxygen wafer doped with nitrogen, a minute defect of 25 nm or less such as a “cavity” cannot be detected by the current defect evaluation method.

  The present invention has been made in view of such problems, and it is possible to detect a crystal defect that can detect a crystal defect that is present in a low oxygen concentration silicon single crystal wafer doped with nitrogen and that is particularly small in size. It aims to provide a method.

  The present invention has been made to solve the above-mentioned problems, and is a method for detecting crystal defects existing in a silicon single crystal wafer having an initial oxygen concentration of 8 ppma (JEIDA) or less doped with nitrogen, the silicon single crystal wafer being Performing a heat treatment in an oxygen atmosphere to inject oxygen into the crystal defects, revealing crystal defects having a defect size of 25 nm or less, and enabling detection of the crystal defects after the heat treatment. A ratio of oxygen solid solubility and initial oxygen concentration of the silicon single crystal wafer at the time of the heat treatment is α = oxygen solid solubility / initial oxygen concentration. There is provided a crystal defect detection method, characterized in that the heat treatment temperature in the heat treatment is set so as to be in the range of 3 or less.

  In this way, by heat treatment in which the heat treatment temperature is set so that α is in the range of 1 to 3, the majority of crystal defects having a defect size of 25 nm or less can be made manifest and detectable. By detecting this actual crystal defect, the crystal defect whose defect size is 25 nm or less can also be detected.

  In this case, it is preferable that the heat treatment temperature is 900 ° C. to 1200 ° C., and the heat treatment time is 10 to 60 minutes.

  With such a heat treatment temperature and heat treatment time, crystal defects of the silicon single crystal wafer can be manifested more reliably.

Further, the present invention is suitable when the nitrogen dope concentration of the silicon single crystal wafer is 1 × 10 ¹³ to 1 × 10 ¹⁵ atoms / cm ³ .

  In such a nitrogen-doped silicon single crystal wafer, since the size of the crystal defect is particularly small, the method of revealing and detecting the crystal defect according to the present invention is particularly effective.

  In the present invention, the crystal defect can be detected by any one of detection by a light scattering type particle counter, detection by a laser microscope of a confocal optical system, and detection by an RIE method.

  By such a method, the crystal defect manifested by the present invention can be detected.

  With the crystal defect detection method according to the present invention, crystal defects with a small defect size should be made obvious and detectable even in a low-oxygen wafer doped with nitrogen, particularly with a small defect size. Can do. By detecting the actual crystal defects, defects having a defect size of 25 nm or less can also be detected. As a result, the crystal defects of the low oxygen wafer doped with nitrogen can be more accurately evaluated.

It is a conceptual diagram which shows the model which can reveal a crystal defect by the method of this invention as one of the models explaining the behavior of the crystal defect by heat processing. It is a conceptual diagram which shows one of the models explaining the behavior of the crystal defect by heat processing. It is a conceptual diagram which shows one of the models explaining the behavior of the crystal defect by heat processing. It is a conceptual diagram which shows one of the models explaining the behavior of the crystal defect by heat processing. In an Example and a comparative example, it is an image at the time of detecting a surface defect using MAGICS by Lasertec.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

  First, a mechanism that enables detection of crystal defects in the present invention will be described.

  As described above, in the case of a silicon single crystal wafer having a low oxygen concentration (low oxygen wafer), there is a problem that it is difficult to detect minute crystal defects such as BMD, COP, and “cavity”. In particular, since the defect size becomes smaller in a low-oxygen wafer doped with nitrogen, a minute defect of 25 nm or less such as a “cavity” cannot be detected by the current defect evaluation method.

  High sensitivity evaluation methods for detecting defects in minute BMDs and COPs include RIE (Reactive Ion Etching) by reactive ion etching, and methods for inspecting a wafer cross section by laser scattering (for example, crystals manufactured by Raytex) And the like using a defect inspection apparatus MO441.

  The RIE method has a detection lower limit of about 10 nm and is effective for detection of minute BMDs, but has a problem that a COP with a thin inner oxide film is not detected even if the size is larger than the detection lower limit.

  On the other hand, in the case of the laser scattering method for the wafer cross section, information on the wafer surface layer could not be obtained, and it was applicable only to bulk defect evaluation. Further, there is a problem that the area to be evaluated is narrow and the in-plane distribution of crystal defects cannot be evaluated.

  Therefore, in the present invention, first, a silicon single crystal wafer is heat-treated in an oxygen atmosphere to inject oxygen into minute crystal defects to form an inner surface oxide film in the minute defects, and to increase the defect size. , Make it manifest. Next, the crystal defects that have become apparent after the heat treatment are detected by a predetermined method.

  Oxygen injection in the heat treatment for revealing crystal defects must be such that the oxygen solid solubility of the silicon single crystal wafer at the heat treatment temperature is equal to or higher than the initial oxygen concentration of the wafer (oxygen solid solubility ≧ initial oxygen concentration). It is a condition. That is, if the solid solubility of oxygen in the wafer is low, oxygen cannot be injected into the crystal defects.

  As the heat treatment temperature increases, the oxygen solid solubility of the wafer increases and oxygen is easily injected into the wafer.

  However, if the heat treatment temperature is too high, even if oxygen is injected into the wafer, the crystal defects diffuse out in the temperature rising stage, or the crystal defects disappear when the size is small (if much smaller than the critical size) Crystal defects cannot be properly evaluated.

  On the other hand, if the heat treatment temperature is too low, the difference between the oxygen solid solubility and the oxygen concentration in the wafer becomes small, and it becomes difficult to inject oxygen into the crystal defects, making it impossible to reveal the crystal defects.

  As a result, it is thought that it is necessary to set an appropriate heat treatment temperature, that is, an appropriate oxygen solid solubility with respect to the oxygen concentration in the wafer, and the oxygen solid solubility / initial oxygen concentration and the behavior of crystal defects The relationship was investigated.

  Here, (1) a model that can reveal crystal defects, (2) an outward diffusion model, (3) an inward diffusion (defect annihilation) model, and (4) a model that does not reveal crystal defects sufficiently. Since there are four models, these models will be described with reference to FIGS.

(1) Model capable of revealing crystal defects With reference to FIG. 1, a model capable of revealing crystal defects will be described. As will be described later, this model is established when 1 ≦ α (= oxygen solid solubility / initial oxygen concentration) ≦ 3.

  FIG. 1A shows the crystalline state of the silicon single crystal wafer before the heat treatment. There are crystal defects such as COP, BMD, and cavities, and as COPs, there are particularly small-sized and thin oxide films.

  Changes in crystal defects during the heat treatment (heat treatment stage) of the silicon single crystal wafer will be described by dividing into a temperature rising stage in FIG. 1 (b-1) and an oxygen diffusion stage in FIG. 1 (b-2). In the temperature raising stage, an oxide film is formed on the wafer surface by oxygen in the atmosphere, and interstitial silicon is generated in the wafer. The introduction of interstitial silicon tends to make the COP oxide film thinner or to reduce cavities, but it does not disappear. In the next oxygen diffusion stage, the inner surface oxide film of COP becomes thicker due to the implantation of oxygen in the atmosphere, the size of BMD increases, and the oxide film is formed on the inner surface of the cavity. Thereby, each crystal defect becomes obvious.

  As described above, the crystal defects are manifested by the heat treatment in the oxygen atmosphere, and the manifested crystal defects can be detected as shown in FIG.

  In addition, the dotted line in FIG. 1 represents the change of the oxygen concentration compared with the stage before heat processing in the figure. A region where crystal defects become apparent is a region where oxygen is implanted (a region where the oxygen concentration is shown to be higher than that before heat treatment by a dotted line representing the oxygen concentration).

(2) Outward diffusion model A model in which oxygen diffuses outward will be described with reference to FIG. As will be described later, this model is established when oxygen solid solubility / initial oxygen concentration = α <1.

  FIG. 2 (a) shows the crystal state before the heat treatment, as in FIG. 1 (a).

  FIG. 2B shows the heat treatment stage. When the oxygen concentration of the silicon single crystal wafer is higher than the oxygen solid solubility of the wafer, an oxide film is formed on the surface, interstitial silicon is generated, and outdiffusion of oxygen existing on the wafer surface layer occurs. As a result, the following phenomenon occurs. First, due to the outward diffusion of oxygen, the COP inner surface oxide film is melted and becomes a cavity. Moreover, the cavity is filled and becomes smaller by the implantation of interstitial silicon. In addition, small cavities are filled and crystal defects disappear. For this reason, since the defect state and the number of defects on the wafer surface layer portion are changed, accurate defect evaluation cannot be performed as it is.

  In addition, the dotted line in FIG. 2 represents the change of the oxygen concentration compared with the stage before heat processing in the figure. As shown in the figure, oxygen in the surface layer portion is diffused outwardly and decreased.

(3) Inward diffusion (defect annihilation) model With reference to FIG. 3, a model in which oxygen diffuses inward and crystal defects disappear will be described. As will be described later, this model is established when oxygen solid solubility / initial oxygen concentration = α> 3.

  FIG. 3 (a) shows the crystal state before the heat treatment, as in FIGS. 1 (a) and 2 (a).

  Changes in crystal defects during the heat treatment (heat treatment stage) of the silicon single crystal wafer will be described by dividing into a temperature rising stage in FIG. 3 (b-1) and an oxygen diffusion stage in FIG. 3 (b-2). When the defect size is small and the cavity exists in the wafer, crystal defects smaller than the critical size disappear at the temperature rising stage of (b-1). In the oxygen diffusion stage, the formation of the surface oxide film is promoted, and the implantation of interstitial silicon becomes dominant, so that the cavity is filled and the cavity defect disappears.

  In addition, on the wafer surface layer, crystal defects larger than the critical size are slightly dissolved in the temperature rising stage. However, crystal defects grow with the inward diffusion of oxygen (the COP inner surface oxide film becomes thicker, an oxide film is formed on the inner surface of the cavity, and BMD also grows).

  The dotted line in FIG. 3 represents the change in oxygen concentration compared to the pre-heat treatment stage. A region where crystal defects become apparent is a region where oxygen is implanted (a region where the oxygen concentration is shown to be higher than that before heat treatment by a dotted line representing the oxygen concentration).

  In this model, surface layer defects may disappear as described above, so accurate evaluation is possible when evaluating surface layer defects using a light scattering type particle counter or a confocal optical laser microscope after heat treatment. Can not.

(4) Model in which crystal defects are not sufficiently manifested With reference to FIG. 4, a model in which crystal defects are not sufficiently manifested when the heat treatment temperature is too low will be described. FIG. 4A shows the crystal state before the heat treatment, as in FIGS. 1A, 2A, and 3A.

  FIG. 4B shows the heat treatment stage. When the heat treatment temperature is too low, the growth rate of the surface oxide film is slow and the generated interstitial silicon is small, so that COP, BMD, and cavities do not disappear even if the size is small. In addition, since the oxygen diffusion coefficient is small, only a small amount of oxygen is injected into the wafer surface layer. As a result, the original wafer state is not affected even after the heat treatment, and the crystal defects are not effective. That is, the wafer in the measurement stage of FIG. 4 (c) has little change compared to the initial wafer of FIG. 4 (a).

  The dotted line in FIG. 4 represents the change in oxygen concentration compared to the pre-heat treatment stage.

(Experiment)
In order to obtain the optimum value of α = oxygen solid solubility / initial oxygen concentration for the manifestation of crystal defects (among the above models, (1) a value applicable to a model capable of revealing crystal defects), the following experiment Went.

  The relationship between the heat treatment temperature and oxygen solid solubility of the nitrogen-doped wafer and the various substrate oxygen concentrations (1, 3, 5, 8, 10 ppma (JEIDA)) are various heat treatment conditions (temperature: 900, 1000, 1100, At 1200, 1250 ° C., time: 30 minutes, oxygen atmosphere), by using a laser microscope with a confocal optical system (MAGICS, manufactured by Lasertec Corporation), the presence or absence of crystal defect detection is determined. We estimated which model was applicable.

  From the above experiment, the relationship of α = oxygen solid solubility / initial oxygen concentration capable of revealing defects was derived. The results are shown in Table 1 below. In Table 1, the symbol [◯] indicates the case where the crystal defects are increased compared to the pre-heat treatment stage, and the symbol [×] indicates the case where the crystal defects are reduced or eliminated compared to the pre-heat treatment stage. ing. Further, when α <1, it is estimated that (2) it corresponds to the outward diffusion model, and when α> 3, it is estimated that it corresponds to (3) the inward diffusion (defect annihilation) model. In addition, it is estimated that (4) the model in which the crystal defects are not sufficiently manifested appears at a heat treatment temperature much lower than this example.

  As a result, when α = oxygen solid solubility / initial oxygen concentration, if the heat treatment conditions are selected so that α is in the range of 1 to 3, even if it is a nitrogen-doped low oxygen concentration silicon single crystal wafer It was found that proper defect evaluation is possible.

  From the above viewpoint, in the present invention, heat treatment is performed in an oxygen atmosphere as follows in order to reveal crystal defects present in a silicon single crystal wafer having an initial oxygen concentration of 8 ppma (JEIDA) or less doped with nitrogen. That is, when the ratio of the oxygen solid solubility of the silicon single crystal wafer and the initial oxygen concentration during the heat treatment is α = oxygen solid solubility / initial oxygen concentration, the heat treatment is performed so that α is in the range of 1 to 3. By setting the heat treatment temperature in and performing heat treatment on the silicon single crystal wafer in an oxygen atmosphere, oxygen is implanted into the crystal defects, and crystal defects having a defect size of 25 nm or less are made obvious and detectable. As a result, the majority of crystal defects having a defect size of 25 nm or less can be manifested and detected. By detecting this actual crystal defect, the crystal defect whose defect size is 25 nm or less can also be detected.

  By setting the temperature to 900 ° C. to 1200 ° C. and the time to 10 to 60 minutes as the heat treatment conditions for revealing crystal defects, an appropriate oxygen solid solubility can be obtained and oxygen can be injected into the crystal defects. As a result, the crystal defects of the silicon single crystal wafer can be manifested more reliably.

The present invention can be applied to a nitrogen-doped low oxygen wafer, but is particularly suitable when the nitrogen doping concentration is 1 × 10 ¹³ to 1 × 10 ¹⁵ atoms / cm ³ . In such a nitrogen-doped silicon single crystal wafer, since the size of the crystal defect is particularly small, the method of revealing and detecting the crystal defect according to the present invention is particularly effective.

  As a method of detecting the crystal defects that have become apparent in this manner, a known method can be appropriately employed. In particular, detection can be performed using detection using a light scattering particle counter, detection using a confocal optical laser microscope, detection using an RIE method, and the like. For example, an apparatus such as SP-1 manufactured by KLA Tencor can be used as a light scattering type particle counter, and MAGICS manufactured by Lasertec can be used as a laser microscope of a confocal optical system.

  Further, in order to detect a crystal defect that has become apparent according to the present invention, an oxide contained in the crystal defect that has become apparent may be removed by HF etching. The oxide contained in the crystal defects manifested here is, for example, a thickened oxide film on the inner surface of the COP, BMD (that is, oxygen precipitate), an oxide film formed on the inner surface of the cavity, or the like. is there.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this does not limit this invention.

(Examples 1-3, Comparative Examples 1-3)
First, a diameter of 200 mm, an oxygen concentration of 4 ppma (JEIDA), a nitrogen concentration of 3 × 10 ¹³ atoms / cm ³ , a V region (a region having many vacancies), and a vacancy is an atomic level generated due to a shortage of silicon atoms 6 pieces of silicon single crystal wafers were prepared by cutting out from the same silicon single crystal ingot.

  Next, of these five wafers, for oxygen solid solubility and initial oxygen concentration, α = oxygen solid solubility / initial oxygen concentration is 0.75 (Comparative Example 2), 1 (Example 1), The heat treatment was performed by adjusting the heat treatment conditions so as to be 1.5 (Example 2), 3 (Example 3), and 3.5 (Comparative Example 3). For comparison, one of the prepared six wafers was not subjected to the apparent heat treatment (Comparative Example 1). Specific heat treatment conditions were performed in an oxygen atmosphere, and the temperature and time were as shown in Table 2 below.

  Crystal defects of each of the wafers of the examples and comparative examples after heat treatment (comparative example 1 was not heat-treated) were evaluated using a laser microscope (MAGICS manufactured by Lasertec Corporation) of a confocal optical system.

  FIG. 5 shows an image of the surface defect detection result. In Examples 1 to 3, that is, when α is 1, 1.5 and 3 respectively, more crystal defects are detected compared to the wafer not subjected to the heat treatment (Comparative Example 1), and minute crystal defects are detected. It was found that it was manifested. On the other hand, in Comparative Examples 2 and 3, that is, when α is 0.75 and 3.5, respectively, the crystal defects are reduced as compared with the wafer (Comparative Example 1) that is not subjected to the heat treatment, and the crystal defects become apparent. The purpose of could not be fulfilled.

The above results are summarized in Table 2 below.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Claims (4)

A method for detecting crystal defects present in a silicon single crystal wafer doped with nitrogen and having an initial oxygen concentration of 8 ppma (JEIDA) or less,
Performing a heat treatment in an oxygen atmosphere on the silicon single crystal wafer to inject oxygen into the crystal defects, and to make crystal defects having a defect size of 25 nm or less manifest and detectable;
Detecting a crystal defect of the silicon single crystal wafer after the heat treatment,
When the ratio of the oxygen solid solubility and the initial oxygen concentration of the silicon single crystal wafer during the heat treatment is α = oxygen solid solubility / initial oxygen concentration, α is in the range of 1 or more and 3 or less. A method for detecting a crystal defect, characterized by setting a heat treatment temperature in the heat treatment.   2. The crystal defect detection method according to claim 1, wherein the heat treatment temperature is set to 900 [deg.] C. to 1200 [deg.] C., and the heat treatment time is set to 10 to 60 minutes. The method for detecting a crystal defect according to claim 1, wherein a nitrogen dope concentration of the silicon single crystal wafer is set to 1 × 10 ¹³ to 1 × 10 ¹⁵ atoms / cm ³ .   The detection of the crystal defect is performed by any one of detection by a light scattering type particle counter, detection by a laser microscope of a confocal optical system, and detection by an RIE method. The method for detecting a crystal defect according to any one of the above.